1. Field
The present specification generally relates to methods for forming glass sheets from continuous glass ribbons and, more particularly, to methods of scoring and separating glass sheets from continuous glass ribbons.
2. Technical Background
Continuous glass ribbons may be formed by processes such as the fusion draw process or other, similar downdraw processes. The fusion draw process yields continuous glass ribbons which have surfaces with superior flatness and smoothness when compared to glass ribbons produced by other methods. Individual glass sheets sectioned from continuous glass ribbons formed by the fusion draw process can be used in a variety of devices including flat panel displays, touch sensors, photovoltaic devices and other electronic applications.
Continuous glass ribbons formed by the fusion draw process often bow or curve in a lateral direction due to temperature gradients in the glass as it cools. After the glass ribbon is drawn, individual sheets of glass are sectioned from the ribbon by supporting the glass ribbon with a nosing device as the glass ribbon is scored and separated along the scoring line. When a flat nosing device is used to support the continuous ribbon during scoring, engaging the scoring device with the curved glass ribbon tends to flatten the glass ribbon thereby introducing stress into the glass ribbon which may distort or break the glass ribbon during scoring. The contact between the scoring device and the curved glass ribbon also introduces motion in the ribbon which is propagated upstream of the scoring device and causes undesirable stress and warp in the ribbon. When a bowed nosing device (i.e., a nosing device which is curved to match the curvature of the glass ribbon) is utilized, stresses and ribbon motion introduced during the scoring operation are reduced as the curved nosing device conforms to the contours of the glass ribbon thereby supporting the glass ribbon and preventing the glass ribbon from being flattened against the nosing. However, when a bending moment is applied to the glass ribbon to bend the glass ribbon against the curved nosing and separate a glass sheet from the glass ribbon at the score line, the curved glass ribbon is constrained against the curved nosing and, as a result, stress is introduced in the glass in the nosing contact area which causes unwanted breakage of the glass sheet and/or the glass ribbon adjacent to the score line. While this type of uncontrolled breakage occurs in glass ribbons of all widths, the problem is particularly prevalent for glass ribbons of larger widths (i.e., widths of 1.5 meters or greater).
Accordingly, a need exists for alternative methods of separating glass sheets from continuous glass ribbons to prevent unwanted breakage.